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LM5050-2: LM5050-2 with acoustic noise issue

Part Number: LM5050-2

Hi,

Customer reported the TI LM5050-2 has noise when they have about 12V/3A input condition which is from the adapter, and the waveform is as attached for your reference.

The gate pin of LM5050-2 has a 10KHz frequency, it’s in the audio frequency and could be heard.

Can you please help to comment?

 

The attachment is the waveform, the schematic, and the Board file for your reference.

Blue is GND, White is +15V_VIN0, Orange is +15V_VIN1, Green is +15V_VIN2, Red is LM5050_0_OUT & LM5050_1_OUT

Purple is LM5050_0_G & LM5050_1_G.

 

Ideal diode For TI review only.pdf

Brd for TI review.7z

Best regards,

Randy

  • Hello Randy,

    I have looked in detail at the waveforms and the schematic.

    One reason why this issue on gate oscillations could be due to ripple or noise on the output of LM5050-2.

    If the output of LM5050-2 (+15V_VIN2 rail) is connected to the DC/DC converter and noise on the input of DC/DC due to switching can cause +15V_VIN2 to have noise or ripple. This noise if exceeds the reverse threshold 27mV of LM5050-2 will cause the LM5050-2 gate to turn off and on based on the noise.

    From the schematic, we see that there is not capacitor on the output (need to be placed close to IC) to filter the noise of downstream DC/DC converter affecting LM5050-2 operation.

    Can you confirm if there is a DC/DC converter or any circuit that can cause noise (10kHz) into the Output of LM5050-2 (+15V_VIN2)?

    If yes, then adding or increasing the capacitance 1uF or higher on the output to GND of LM5050-2 will certainly help to resolve this isssue.

    Regards,

    Kari.

  • Hi Randy,

    We are taking this discussion over email.

    Regards,
    Kari.

  • Hi Randy,

    One way to resolve this issue is to increase the value of resistance PR9647 and PR9649 from 0ohm to 40ohm.

    This shift the regulation threshold from 16mV to 5.6mV and change the reverse threshold from -27mV to -37.4mV.

    This will avoid the noise and prevent turn on/off that is happening at light load.

    Regards,
    Kari.